DC motor speed

[Badger110]

I picked up some linear actuators for my roof project, they weren't expensive so i wasn't expecting them to be amazing, however they will do what i want them to do but they are a tad slow.

400mm extended takes 1min and 20 seconds with a direct 12v feed. This is under no load. ( imagine the scene from Despicable Me when the old guy goes to leave everyone on his motorized scooter. It feels that slow )

I have seen speed controllers but i can't see how a speed controller can make the motor work any quicker when it's already pulling 12v from the battery, but perhaps i have this wrong? 

I'm not that clued up  when it comes to motors n power stuff, can anyone explain the simple terms of increasing the speed of the motor, if at all possible?

Increase in voltage ?

 

other options are to change the gearing, but i haven't taken one apart just yet to see if this is possible

 

 

[lo-fi]

Without going into the long, short and curlys of it, the only way you'll increase the speed they go at will be feeding them more voltage. A speed controller can only slow them down, unless it's got some kind of clever dc-dc inverter and bumps the output voltage. You're onto a loser with changing the gear ratio too if you want to maintain the same force applied. Running at higher voltage has its perils, meaning more current and more heat. 

Your options here are to live with the slowness, bump the voltage by series-ing in another battery to that circuit, or dishing out for better actuators. The Chinese ones essentially just use horrid little low power motors (as that's the expensive bit) geared so low that they get a decent amount of push/pull. 

I think I'd put it down to experience and find something better myself. You're essentially paying for the motor, so look at the motor specs when choosing. More current = more power = more better, and should be faster assuming not geared crazy low for uber force. 

Hope that makes it a bit clearer! 

 

[Badger110]

Perfectly explained, thank you lo fi 👍

[Bowie69]

If using with the engine running. It will be a little faster, as it will be getting more like 14V, which can make quite a difference. 

You could try it with a dc-dc converter, maybe up to 16V without risk or burning it out. 

I expect if you check the specs of the actuators they will have a speed on them mm/minute or similar, you may find the lighter duty ones have higher gearing and are therefore faster - think you said yours are rather overspec for lifting capacity? 

[Badger110]

They say 5.7mm sec rated at 150kg lifting so they are  over specced for the amount they are lifting (65kg between 2 of them ).

However I’ve not fitted them as yet so I’m only going on the short bench test. 
 

I did a quick check on a 18v battery and the speed is much better which is to be expected 

 

 

[cackshifter]

There are DC to DC  ('boost')converters that will increase the voltage and aren't very expensive. AS the motor is only going to run for a moment, maybe heat isn't a factor as long as you don't go crazy - think of starters for instance that'll only work 30 seconds before needing a rest. If you do go this route I suggest you operate well within the current rating of the converters, and either have 2 converters or arrange it so you can easily take it out of circuit just in case of Chinese electronics suffering a premature death.

[philthespark]

If you are going to start getting involved with converters, be very careful, avoid the chinese tat! Over the years I've done a fair bit with inverters and variable speed drives etc on big plant, it works ok until people start buying cheap stuff, most decent stuff has a built in redundancy factor, if it says 100 watts, for example, you can generally run it at about 150 watt for short periods, although I don't recommend it. the cheap stuff though is usually rated at peak load, I've had it with people wanting inverters in vans to run say a drill or grinder. They see one online that says 1000w inverter for say £40 and buy it, the first time they use it it trips out! It's about this time that they start to learn about inrush, or start up currents as they are sometimes known, it may say it's a 1000w inverter, but you'll be lucky to run anything bigger than a lightbulb off some of them, it's the same with trying to run them on the go, I tested a few cheaper ones when the lads wanted to charge their cordless drill batteries on the go, most ran fine until you started the engine, then went into lockout, when they say 12v they mean it, top end, not the 13 or 14 volts you get with the engine running, it's definately a case of buy cheap buy twice, with a lot of this chinese stuff. Incidentally it's very much the same with generators, there's one particular model doing the rounds that not only has 110 and 240 sockets on it, but also a 415v 3 phase, absolutely useless, they were rated at over 3Kw IIRC, in tests they were putting out less than 1Kw,  cheap generators were something I had the dubious pleasure of dealing with back in my equestrian days, for some reason horsey people will spend daft money on a pair of  'trendy' pink wellies, or some other such garbage, but start moaning when you tell them they need to spend about a grand on a decent generator for their stables. lol